1. Field of the invention
This invention relates to a process for preparing organic smectite which is mainly applied for thickener used for grease, printing ink, lipophilic paint, synthetic resin paste and the like, protective colloid, dispersant and binder.
2. Description of the prior art
Processes for preparing organic bentonite made by olephilization of bentonite (sodium salt and/or calcium salt of montmorillonite), which is one kind of smectite, have been studied for a number of years. At first, C. R. Smith in 1934 produced a composite by combining the bentonite with an organic compound (J. Am. Chem. Soc., 56, 1561, (1934)), and this process was patented (C. R. Smith: U.S. Pat. No. 2,033,856 Mar. 10, 1936). Since then, the study of organic bentonite was made more closely by S. B. Hendricks (J. Am. Chem. Soc., 62, 1457 (1940)), J. W. Jordan (J. Phys. & Colloid Chem., 53, 294 (1949)) and E. A. Hauser (U.S. Pat. No. 2,531,427 Nov. 28, 1950)
All of these processes comprise the following steps; At first, bentonite is dispersed into water to be swollen and is purified by a hydraulic elutriation to form a suspension. Then, an aqueous solution including organic cations is added to the suspension to produce a condensed precipitate. Then, by filtering, dehydrating, drying and finely powdering the precipitate, organic bentonite is produced. In order to supply the organic cations for this process, aliphatic amine salts such as octadecylamine acetate C.sub.18 H.sub.37 NH.sub.2.sup.. HOCOCH.sub.3 and quaternary ammonium salts such as dimethyldioctadecylammonium chloride (C.sub.18 H.sub.37).sub.2 N(CH.sub.3).sub.2.sup.. Cl were used as organic compounds.
Organic bentonite was firstly on the market as Benton (trade name) by National Lead Co., USA in the 1950s, then, it has been commercially available also in Japan as Orben (trade name) by Shiraishi Industry Co. Ltd., Japan, Organite and S-Ben (trade names) by Hojun Mining Industry Co. Ltd., Japan, and the like until the present.
The process for preparing organic bentonite has been carried by a liquid-liquid reaction between a suspension including bentonite which is one kind of smectite and an aqueous solution of organic amine. By the liquid-liquid reaction, alkaline metal ions or alkali earth metal ions in the interlayer spaces of montmorillonite which is a main component of the bentonite are exchanged for organic amine ions. The reason why the liquid-liquid reaction has been used is as follows. According to the above mentioned process by C. R. Smith et al., after the bentonite in water is purified by a hydraulic elutriation, the aqueous solution containing the bentonite must be filtered in order to be used for obtaining the organic bentonite. In this case, the method of filtering the aqueous solution of the swollen bentonite is very difficult. Compared with this method, the method of filtering a precipitated product obtained by reacting the suspension of the bentonite with the aqueous solution of the organic amine is easier. In addition, it is natural for all of those who have studied this field to come up with only the liquid-liquid reaction, because this field began with the finding of the phenomenon of ion exchange in the 1930s. Therefore, the solid-solid reaction between the particles of the smectite and that of the organic amine has not been considered until the present.
On the other hand, it was reported that kaolinite, which has a different crystalline structure from that of bentonite, can form intercalation compounds by a solid-solid reaction, that is by grinding the powder mixture of kaolinite and potassium acetate by K. Wada (Am. Mineral, 46. 78 (1961)). However, in this case, it requires a whole day to finish the reaction.
Clay et al. (U.S. Pat. No. 4,474,706) disclose the dry process for the production for an organophilic clay. However, the dry process in this Patent does not mean a solid-solid reaction but a water free process in which melted organic ammonium salts are reacted with a dry clay. In this process, the reactants are mixed or blended at elevated temperature, e.g. temperature ranging up to 60.degree. C. or higher, so that the ammonium salts are in liquid form and mixing of the reactants is rigourous. Therefore, this process is distinguished from the solid-solid reaction.
Moreover, in the field of medicine, there have been reports about the intercalation reactions between smectite and specific medicines by M. A. Vincente et al. (Clays & Clay Miner., 37, 157 (1989)) and Y. Nakai et al. (Chem. Pharm. Bull. 34 (11), 4760-4766 (1986)). However, these kinds of reaction are rather adsorptions of the medicines than a solid. solid reaction. Further these kind of reaction have different object from that of the solid-solid reaction of the present invention.
As a result, there has been no report related to the solid-solid reaction producing the organic smectite which is applied to thickener, protective colloid, dispersant and binder provided by the present invention.
The conventional process for preparing the organic smectite by the liquid-liquid reaction has following problems. The conventional process requires the step in which bentonite minerals are dispersed in water, swollen and purified by a hydraulic elutriation to form a suspension required for the liquid-liquid reaction. Further, the conventional process has a problem related to environmental pollution as for the treatment of waste water and industrial waste caused from the step in which the swollen bentonite is purified by the hydraulic elutriation. Moreover, in the liquid-liquid reaction, an organic guest substance is intercalated in the interlayer spaces of host bentonite, after the crystalline structure of the host bentonite is broken once. Accordingly, irregular stacking is caused in the composite of organic bentonite and the product has low crystallinity.